Within telecommunications, data is transmitted wirelessly over radio frequency. The radio link performance is limited by the amount of noise and interference. Noise generally relates to an error or undesired random disturbance of the data signal. Noise can be introduced by natural (e.g., thermal noise) and/or man-made sources (e.g., emitted energy). However, noise is typically distinguished from interference (e.g. cross-talk, unwanted leakage from nearby transmitters, etc.), which is the addition of an unwanted signal to the data signal. Both noise and interference degrade the performance of radio links; however, certain qualities of interference can be exploited to reduce its effects.
Some techniques for interference reduction are based on avoiding interfering situations (e.g., time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), etc.). Unfortunately, multiple access schemes are generally inefficient in terms of throughput per resource because resources cannot be “reused” between users.
Other techniques reduce the interference level such that it can be treated as background noise; for example, at overlapping cell boundaries, only one cell is allowed to transmit with high power, while the other cell(s) are restricted to lower power. Unfortunately, interference reduction techniques impose transmit power constraints which can reduce throughput per user.
Still other techniques amplify interference such that it can be detected and removed. Successive interference cancellation is one typical example of an interference amplifying scheme. Drawbacks for successive interference cancellation include e.g., increased decoding complexity, and error propagation.
Hence, improved methods and apparatus are needed to improve transmission and/or reception performance in wireless systems.